This East Coast city was the home of $387.17 million in greentech projects last year, representing a gain of 6.8% from 2007. The city is also host to a $500 million solar initiative and a $2 million affordable green housing project, as well as numerous cleantech companies like Boston Power, EnerNoc, and 1366 Technologies.

2. Denver

Home to more than just altitude junkies, this city has the first major airport to reach strict 14001 standards. Denver is also home to the world's biggest wind turbine maker, Vestas, along with solar company Conergy. Neighboring Boulder is also set to become the country's first smart grid city.

3. Seattle

Seattle is aiming to become a cleantech R&D hub, with up to $200 million in stimulus funds expected to help further its goal. The city also consistently ranks among the top three U.S. cities cities with the largest number of certified green buildings, and is already home to cleantech companies like Helion, PowerIt, and Propel Fuels.

4. Austin

The home of South by Southwest is also the new headquarters for the Clean Technology and Sustainable Industries Organization (CTSI), which works on research in green transportation, construction, electricity generation, greenhouse gas reduction, and industrial energy efficiency. Local utility Austin Energy is also planning to develop a research consortium to work on smart grid and smart metering project.

5. San Francisco

The City by the Bay is host to a slew of big-name cleantech companies, including GreenVolts, Arch Rock and Grid Net. San Francisco also hosts the Clean Tech Open, a yearly clean technology business competition that offers prize money and the opportunity to network with connect with venture capitalists.